The pharmacological action of caffein as it relates to the normal man and animal has been for many years the subject of extensive research. Its main effects on the normal cardiovascular and nervous systems are well known. Briefly stated for the purpose of this paper, this effect of caffein in moderate doses is, first, to produce a moderate rise of blood-pressure due to a stimulant action on the heart muscle (this rise is maintained in spite of a mild degree of vasodilatation) ; second, an increased urinary output due to circulatory changes, and third, an increased respiratory rate. The cerebral functions are stimulated and the muscle tone increased. This experimental field was reviewed and the varying results of the different investigators harmonized by Sollmann and Pilcher1 in 1911.
With this action in mind the pharmacologists have given the drug a high therapeutic rating and it
TAYLOR L. CLINICAL STUDIES IN CAFFEIN. Arch Intern Med (Chic). 1914;XIV(6):769-778. doi:10.1001/archinte.1914.00070180002001